The present invention relates to an actuator for an ink jet printer.
An actuator for an ink jet printer is an ink pump of a print head used for an ink jet printer. An actuator having a structure as shown in FIG. 3 has generally been used. In FIG. 3, an actuator 1 for an ink jet printer is constituted of an ink tank 28 and a piezoelectric/electrostrictive working portion 26. The ink tank 28 is obtained by unitarily forming a thick substrate 21 having a cavity 20 and a vibrating plate 22 covering the cavity 20. The piezoelectric/electrostrictive working portion 26 is constituted of a piezoelectric/electrostrictive layer 24, the upper electrode layer 25 formed on the upper surface of the piezoelectric/electrostrictive layer 24, and the lower electrode layer 23 formed on the lower surface of the piezoelectric/electrostrictive layer 24. The piezoelectric/electrostrictive working portion 26 is disposed on the ink tank 28 so that the lower electrode layer 23 contacts with the vibrating plate 22 of the ink tank 28.
When an electric field is generated between the upper electrode layer 25 and the lower electrode layer 23, a piezoelectric/electrostrictive layer 24 made of a piezoelectric/electrostrictive functional member is transformed and a capacity of the cavity 20 is decreased. Accordingly, ink with which the ink tank 28 is filled is jetted out of a nozzle hole (not shown) being connected with the cavity 20 for printing. An ink jet printer is formed by appropriately disposing a predetermined number of actuators 1 having such a structure.
In such an actuator for an ink jet printer, variance in ink jet volume cause variance in a size of a dot upon printing, and an image having high quality cannot be obtained. Accordingly, it is necessary to uniformalize an ink jet volume from each nozzle hole. For example, Japanese Patent Laid-Open 61-118261 discloses a multi-nozzle head for an ink jet printer, in which an electrode surface of a piezoelectric element for promoting vibrations of a head is trimmed so as to change impedance of the piezoelectric element, thereby uniformalizing an ink jet volume.
By the way, in the aforementioned actuator for an ink jet printer, the vibrating plate 22 covering the cavity 20 is thin and is prone to break. Accordingly, when a laser to be generally used for trimming is directly irradiated to the vibrating plate 22, the vibrating plate 22 breaks and its durability deteriorates. Therefore, it is necessary not to irradiate laser directly to the vibrating plate 22. Additionally, a cavity 20, an ink tank 28, and a piezoelectric/electrostrictive working portion 26 are very minute, and it is practically difficult to dispose and form an actuator so that a piezoelectric/electrostrictive layer 24 precisely covers the whole surface of the vibrating plate 22.
Accordingly, the present invention solves the aforementioned problems and aims to provide an actuator for an ink jet printer in which a laser is precisely controlled and only a portion where a piezoelectric/electrostrictive layer covers the vibrating plate is trimmed. Further, the present invention aims to provide an actuator for an ink jet printer, which can conduct trimming by a laser without having breakage of the vibrating plate.